The present invention relates to a process for producing shaped articles of polyethylene terephthalate (hereinafter referred to as "PET") by a low temperature shaping processing.
A high temperature shaping processing process (the term "high temperature" as herein used refers to a temperature above the melting point of PET) such as injection molding, extrusion moulding and the like has been heretofore adopted in the production of PET shaped articles. In the prior shaping process of this type, it was necessary to use a relatively high molecular weight PET whose average molecular weight is in the range of 20000 to 25000 or higher as a not-strengthened, pure PET or to reinforce PET with a significant amount (above 20%) of a glass fiber. However, even if the PET was reinforced in such manner and shaped, the PET had a tendency to be thermally deteriorated during its shaping, thereby resulting in a reduction in the average molecular weight thereof. For this reason, the resulting article was often fragile and non-uniform in quality. Thus, in some instances, it was impossible to produce high quality shaped articles with adequate stability. In addition, this process was costly.
Also, it has been heretofore considered that non-crystalline (not-strengthened) PET shaped articles do not find their suitable applications because of their low temperature (60.degree. to 70.degree. C.) of thermal deformation. Accordingly, no special attention has been paid to a low temperature (a temperature of from room temperature to the softening point of PET (240.degree. C.)) shaping process for non-crystalline PET and a study of this subject has not been made, too, hitherto. Moreover, most of the conventional crystalline or strengthened PET shaped articles were those which were reinforced with a glass fiber. When these FR-PET shaped articles were subjected to a deforming processing at a low temperature, the glass fibers contained therein were cut or it was very difficult to deform the articles. Therefore, the low temperature processing has been considered to be very difficult to carry out. In addition, it was impossible to remove the disadvantages inherent in the PET in the shaped articles.
The inventors have previously made various proposals concerning a high temperature processing (injection moulding, extrusion moulding). As a result of their various studies to overcome the problems associated with such a high temperature processing process and the above described prior problems, the inventors have accomplished this invention.